Project Summary The goal of this project is to define the regulatory networks that control the metabolic function of T lymphocytes under homeostatic conditions and in the context of cancer. Specifically, we aim to identify the differential mechanisms by which distinct T cell lineages sense and respond to nutrient and metabolite signals at steady state (Aim 1) and in experimental models of cancer (Aim 2). Tumor-infiltrating T cells adapt to the tumor microenvironment (TME) by modulating the signaling and epigenetic networks that control their differentiation and function. In line with this notion, T cells can acclimate to metabolic conditions in the TME by altering regulatory mechanisms controlling cholesterol and fatty acid transport, synthesis, and catabolism. Critically, differences in the bioenergetic requirements of antitumor effector T cells and those of suppressive FOXP3+ regulatory T (Treg) may underlie their relative abundance and functionality in the TME. However, the mechanisms by which these distinct T cell subsets sense and respond to the metabolic status of the tumor are poorly understood. We hypothesize that under physiologic conditions and in the tumor setting nuclear receptors serving as sensors of the local metabolic microenvironment can differentially affect the functionality of Treg and effector T cells. To test this hypothesis, we will use targeted genetic and pharmacologic approaches to assess the T cell-intrinsic role of a critical regulator of cellular lipid homeostasis, the liver X receptor (LXR), a sterol- activated nuclear receptor. In preliminary studies, we found that the survival of Treg, but not effector T cells is critically impaired by loss of a single copy of Nr1h2, the gene encoding b isoform of LXR (LXRb). The relative sensitivity of Treg cells to Nr1h2 gene dosage leads us to predict that Treg and effector T cells exhibit differential requirements for LXRb signaling for metabolic fitness. This cell type-specific metabolic vulnerability makes LXRb a potential target for therapeutic manipulation of Treg cell function in tumors. Moreover, because the balance between opposing functions of Treg and effector T cells in the TME determines the outcome of the adaptive anti- tumor response, an understanding of the differential mechanisms by which Treg and effector T cells sense and respond to environmental cues to direct their metabolic function may provide novel avenues for specific targeting of these cells in therapeutic settings. Therefore, our research has the potential to improve clinical care by accelerating the development of novel strategies for immunometabolic intervention in cancer patients.